1. Field of the Invention
This invention relates to a method and apparatus for heating materials with electromagnetic waves, and more particularly, to a control system for electromagnetic heaters. The invention has particular application to the thawing of frozen ground.
Every winter, construction is greatly hindered by frozen ground conditions. Machines presently available for winter excavation are expensive to purchase, expensive to operate and are cumbersome. These machines cannot navigate along complicated trenchlines. Repair work to underground cables and water or gas lines during winter requires the use of jack-hammer and manual labour to excavate the ground around the damaged section. In result, excavation, if attempted when the ground is frozen, results in additional expenses.
2. Description of Related Art
C.P. No. 1,044,331 issued Dec. 12, 1978 to Hamid discloses a microwave horn applicator for use in thawing frozen ground. The applicator is placed on the surface of the ground and radiates energy into the soil. The disclosed apparatus suffers two drawbacks. Firstly, an individual using such apparatus must periodically deactivate the microwave generator and check the depth of penetration of the applicator by manual means to determine whether thawing is complete. Secondly, the applicator itself could overheat and thereby be damaged.
It is also known to insert a waveguide applicator in a material for radiating microwaves into the material in order to heat it--see, for example, U.S. Pat. No. 4,370,534 issued Jan. 25, 1983 to Brandon. However, the known apparatus lacks means to directly determine the extent of the heat treating and means to avoid overheating the applicator.